Quadcopters

History Also known as quadrotors First flying quadrotor: – 11 November 1922 – Etienne Oehmichen Image: blogger.com

History Quadrotors overtaken by helicopters due to workload of the pilot. Some experimental aircraft in the 1950’s Image: San Diego Air & Space Museum ArchivesImage: Wikimedia

Now Increasingly more popular – Unmanned and small – Very maneuverable – Mechanically simple – Electronic stabilization Used for many applications – Photography, inspections, military … toys.

Definitions Roll, pitch and yaw Lift, drag, trust and weight

How does a quadcopter work? 2 pairs of counter rotating motors Roll, pitch and yaw control: – By varying motor speed 12 34

How does a quadcopter work? Roll and pitch Differential thrust Image: pitch forward

How does a quadcopter work? Yaw Differential torque Image: rotate clockwise

How does a quadcopter work? Requires control of the motors Requires (electronic) stabilization: – Due to aerodynamic effects (vortices) – Differences between motors – Weight distribution To do this: – Requires speed controllers – Requires sensors and MCU – Understanding of the forces

How does a quadcopter work? System overview:

How does a quadcopter work? Main components: – Frame – 4 motors and their propellers – 4 speed controllers – Electronic stabilization – Battery – Receiver / other control

Pitch and roll Lift is always perpendicular to the flow direction, in our case the rotor plane. The gravity is always perpendicular to the ground.

Pitch and roll Lift and gravity with pitch and roll. – More lift required – Horizontal lift component provides thrust – When thrust overcomes drag the quadcopter moves.

Pitch and roll Gyro can sense the rotation around the pitch or roll axis. – Unit is rotation in degrees per second. – Integrating this yields pitch or roll angle. Accelerometer can measure gravitational components. – Pitch and roll angle can be calculated with three axes, two per angle (x,z) and (y,z). But….

Pitch and roll Why will this not work well in practice? Gyro’s (especially MEMS and Piezo): – Have a noisy signal – Have an offset (temperature, other effects) – This results in accumulating error in the integration. – Gyro’s can be used for short corrections Accelerometers: – The forces described previously are only in uniform linear motion. – In turns there are more forces due to horizontal lift component.

Pitch and roll When a plane/quadcopter turns it has to roll. This results in a horizontal and vertical lift component. The horizontal lift component gives a centripetal force. The weight and centrifugal force result in cancel out the lift (plane does not climb) This is more commonly known as g-force or load factor. This can be estimated by: For example 30 degree turn is 1.15g The accelerometer will measure this in the Z-axis, the other axes are 0.

Pitch and roll A quadcopter not only has this for roll but also for pitch in sideways movements. How to solve this: – Combine both the gyro and accelerometer information using sensor fusion. – This also makes measurements less sensitive to noise (for example due to vibration).

Yaw Turning around the top-axis. Usually compensated with gyros (short term compensation). Again: drift. For absolute yaw control: use a magnetometer – Basically an electronic compass.

Altitude Can be determined with distance sensors (e.g. ultrasone, laser or infrared) Can be determined with barometric sensors

Lateral drift Two movements you cannot really detect – Optical flow

Local control Keeps the quadcopter stable. Requires sensor fusion – (Extended) Kalman filter – Direct Cosine Matrix – Linear complementary filter

Local control Various control schemes are used by open source projects: Image: IEEE: Build your own quadrotor

Navigation – GPS – Visual servoing (markers) – SLAM – Lidar

TU/e designed quadcopter Optional to use, you can design your own quadcopter. 17 minutes flying time Max. 1 kilogram of payload Component list available Open source software (MultiWII)

TU/e designed quadcopter

MultiWII pro flightcontroller Flightcontroller communicates via bluetooth Can be flown manually with RC controller Sensors: – 3-axis gyro (ITG3205) – 3-axis accelerometer (BMA180) – 3-axis magnetometer (HMC5883L) – Barometer (BMP085) – GPS receiver (MTK3329) Motor RPM counter

TU/e designed quadcopter Cost quadcopter including shipping – Approximately 500 dollar (385 euro) Frame 2 Batteries RC transmitter and receiver 4 Speed controllers 5 Motors (1 spare) Propellers (12 pieces) Flight controller Battery charger + power supply for charger GPS Bluetooth Laser module Beware of taxes and customs fees!

TU/e designed quadcopter Computer vision: – Cubieboard 3 (2-core CPU, 2GB DDR3, 8GB Flash) – Logitech webcam C270 (1280 x 720) – VGA webcam with wide-angle lens

TU/e designed quadcopter Cost vision boards 155 dollar (115 euro) – Cubieboard 3 – Logitech webcam C270 – VGA webcam Wide angle lens Beware of taxes and customs fees!

Lessons learned from last year Try to have your quadcopter built and flying stable as soon as possible. Ultrasound distance sensing is problematic on large quadcopters indoors. Build quality greatly influences stability, sensor noise, etc. Don’t discharge your batteries too much. … no, a raspberry Pi is not fast enough …

Assignments 1.Build your quadcopter and get it flying. 2.Adjust the PID settings and try to find the most stable result. 3.Implement a downward facing camera to compensate for sideways drift and use the laser for altitude control. 4.Task of your choice: marker following, face detection, SLAM, etc.

Questions? Thanks for your attention